A double-pass method is applied to determine the optical image quality in contact lens (CLs) wearers. This is an objective optical non-invasive technique that permits us to test 'in vivo' the optical performance of CLs wearing eyes. The retinal image quality was measured for three subjects wearing two types of monofocal CLs. The results show the effectiveness of the technique to determine the optical performance of the CL and the CL-eye system. The importance of the ocular astigmatism on the MTF is also discussed. In eyes presenting corneal astigmatism, the best results are obtained when wearing RGP CLs. When the astigmatism is corrected, slightly better results were obtained with RGP lenses.